Final answer:
Decreased efflux of potassium ions (K+) is one of the changes in the pacemaker potential of SA node autorhythmic cells, influencing repolarization of the membrane potential.
Step-by-step explanation:
One of the changes that occur in the pacemaker potential related to the SA node, an autorhythmic cell, is a decreased efflux of potassium ions (K+). In the pacemaker potential, conductive cells of the heart start with a slow influx of sodium (Na+) ions, which depolarizes the membrane potential gradually. This spontaneous depolarization (prepotential) continues until the threshold is reached, at which point calcium (Ca²+) channels open and allow for more rapid depolarization. Finally, as the cell reaches approximately +15 mV, Ca²+ channels close, and K+ channels open, allowing potassium to exit the cell, which causes repolarization. Following repolarization, as the membrane potential approaches about -60 mV, K+ channels close.
The reduced efflux of K+ would mean that K+ ions are not leaving the cell as quickly, which would delay repolarization and possibly lead to a prolonged action potential. Thus, autorhythmic cells like those in the SA node rely on a specific sequence of ion movement, including the efflux of K+, to maintain the heart's rhythmic contractions.